In the control of various devices in automotive vehicles and the like, it is common to utilize selectively operated valves to control vacuum or pressure. One type of valve utilized for these purposes is a three port vacuum solenoid valve. When utilized in connection with automotive vehicles, stringent performance requirements are required including temperature limits of operation, such as an operating range over from minus -20.degree. centigrade to +120.degree. centigrade, vacuum and pressure limits of operation, resistant to mechanical shock, electrical capabilities utilizing direct current, functional limits of operation, vibration resistance, resistance to fluids and vapors including gasoline, engine coolant, engine oil, transmission fluid, brake fluid and windshield washer solvent, salt spray, humidity exposure and internal corrosion. In addition, any valve ports must withstand mechanical forces and the electrical terminals must withstand static forces. With respect to performance, it is necessary that such vacuum solenoid valves have specific requirements for vacuum operation including pull-in, drop-out, leakage and flow.
In one type of vacuum solenoid valve of the three port type currently used, the valve comprises three ports and a coil with a core. A plunger within the coil extends into the portion of the body having the ports and supports opposed valves that are movable between spaced seats in the body. In such an arrangement, a greater number of parts are required and alignment of the sealing surfaces is difficult. Furthermore, in operation, the plunger stops at a port face such that the plunger does not reach the magnetic pole face, thereby leaving a residual magnetic air gap that causes higher reluctance in the magnetic circuit and thereby reduces the available mechanical force for sealing. Further, since the plunger is located within the coil, a spring for returning the plunger is positioned within a cavity in both the plunger and the core and this reduction in the magnetic material (iron) further causes higher reluctance in the magnetic circuit and further reduces the available mechanical force for sealing. Finally, this prior arrangement has high fabrication costs and labor costs.
Among the objectives of the present invention are to provide a pneumatic solenoid valve which meets the desired requirements and has improved endurance; improved alignment of sealing surfaces; less reluctance and greater mechanical force for sealing; results in more positive action; utilizes fewer parts; is less costly to fabricate and can be manufactured with greater productivity.
In accordance with the invention, the pneumatic solenoid valve comprises a body having a bore and a first passage intersecting one end of the bore. The bore defines a first seat adjacent the one end. The body has a second passage intersecting the bore intermediate its ends and a third passage. A coil surrounds a core. The core has a fourth passage therethrough with a second seat at one end. A tube provides communication between the other end of the fourth passage and the third passage. A single plunger is provided in the bore and has a first valve at one end adapted to engage the first seat and a second valve at the other end adapted to engage the second seat.